Bimodal neodymium-catalyzed polybutadiene

Process for producing bimodal neodymium-catalysed polybutadienes according to any preceding claim, comprising the steps of:

• 1) modified catalyst production with preforming using catalyst systems based on neodymium consisting of
• component A:
• an alkoxide, a phosphonate, phosphinate and/or phosphate, a carboxylate, a complexed compound of rare earth metals with diketones and/or an addition compound of the halides of the rare earth metals with an oxygen or nitrogen donor compound, preferably neodymium versatate,
• component B:
• a dialkylaluminium hydride, preferably diisobutylaluminium hydride (DIBAH),
• component C:
• a diene, preferably butadiene or isoprene, and
• component D:
• and at least one organometallic halide, preferably ethylaluminium sesquichloride (EASC),
• wherein initially, in a first step, the components A, B and C are mixed at a temperature of −20° C. to 80° C., preferably 0° C. to 40° C., for a period of 5 minutes to 10 hours, preferably 10 minutes to 2 hours, and then the mixture is cooled down to below −10° C., preferably to below −30° C., prior to addition of component D;
• 2) optionally preforming the modified catalyst system at a temperature of −30° C. to 80° C., preferably 5° C. to 50° C., for the duration of 10 minutes to 250 hours, preferably 20 minutes to 100 hours;
• 3) polymerizing the monomers at a temperature between −20 and 100° C.,
• 4) subsequently maintaining the polymerization solution at the end, viz, at a conversion of ≧85% by weight, preferably ≧90% by weight and more preferably ≧95% by weight, of butadiene at a temperature of ≧100° C., preferably 100° C. to 140° C. and more preferably 100° C. to 125° C. for 10 to 120 min, preferably for 15 to 60 min.